In polarized light the lightwaves only move in one
direction. This means that if light moves
through a horisontal filter the light will be horizontaly polarized(HP)
A verticalfilter only lets verticaly polarized(VP) through.
This also means HP. light is blocked by a vertical filter.
The crystals can change the polarization or let light it passunchanged
depending on orientation. This orientation changes if voltage is applied
and thus we can change the light so that it is either blocked or not.
Usualy AC is used sinceDC causes an electrolytic effect and over time
breakes down the liquid.